Diuretic radionuclide assessment of obstruction in the infant: guidelines for successful interpretation

Diuretic renography frequently is used to assess obstruction in hydronephrosis of infancy but it is invalidated by poor renal function, which occurs frequently in this age group. In an attempt to establish a guideline to determine when renal function is too poor in infancy to rely on diuretic renography for an accurate diagnosis we analyzed the slope of the diuretic renographic washout curve of the normal, nonaffected kidney in 33 infants with unilateral hydronephrosis. When the T 1/2 time in the normal, nonaffected kidney was greater than 9 minutes, as occurred in 68 per cent of the infants less than 1 month old, it defined a significant renal functional impairment in both kidneys that interfered with diuretic renographic test interpretation. With time renal function improved and after 4 months of age the T 1/2 time in all nonaffected kidneys became normal and the diuretic renographic diagnosis of obstruction became accurate. Our study indicates that nonaffected kidney T 1/2 time provides a qualitative assessment of global renal function in infancy and defines a level of renal functional maturity that must be achieved to ensure diuretic renographic test accuracy.